1. Field of the Invention
The present invention relates to a data recording device for recording data using a synchronization clock generated on the basis of clock information formed on a recording medium.
2. Description of Related Art
A recording medium such as a magnetic disc or an optical disc is provided with a spiral track 100 as illustrated in FIG. 9, and fine clock marks (hereinafter, referred to as “fcms”), as well as data and address information, are recorded therein (recorded during data writing or preformatted) as clock information (see FIG. 10).
As illustrated in FIG. 9, a disc drive reads the fcms from the recording medium and generates fcm detection signals (hereinafter, referred to as “fcm_pls”). On the basis of the fcm_pls, a PLL circuit generates a synchronization clock (hereinafter, referred to as an “extclk”) and, in synchronization therewith, signals are recorded and reproduced (refer to, for example, JP-A 2000-173194).
However, if there are flaws formed on a recording surface or contamination adhered to the recording surface due to some causes, they may cause the fcms to be detected at different positions from positions at which they are to be detected or to be undetected. This may cause a frequency of the extclk to be higher or lower than a predetermined frequency. Since the disc drive records and reproduces signals in synchronization with the extclk as previously described, when the frequency of the extclk is reduced below a predetermined frequency, recording beyond the end position of a frame (a unit recording region determined by a physical format of the medium; see FIG. 10) into a subsequent frame may occur, which may corrupt data in the subsequent frame.
To cope with this problem, it can be conceived to provide a counter which operates with a reference clock (hereinafter, referred to as a “rfclk”) having a constant frequency such as a quartz oscillator or a synthesizer for knowing the end positions of frames and forcibly stop writing at the end positions of the frames to prevent corruption of data in the subsequent frame.
However, the two clock signals of the rfclk and the extclk are generated by different circuits; therefore, it is difficult to make their frequencies completely the same, thereby inducing frequency errors. Thus, there remains a problem that recording is stopped at a position beyond a frame, which degrades the accuracy of prevention of improper recording, in the case of using a medium having physical formats of large frame lengths and a disc drive.